This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Atoms in a material are rarely still. They jiggle back and forth in collective lattice vibrations known as phonons.
Their motion can also carry a rotational element: In 2023, scientists at PSI experimentally proved the existence of chiral phonons, which exhibit handedness depending on which way they rotate. Now, the same team of researchers has shown that an applied electric field can control the handedness of these phonons. The research is published in the journal Nature Materials.
Whereas the researchers made their initial discovery in quartz, in the latest study they created a tiny device from barium titanate (BaTiO3). This material is ferroelectric, meaning that it possesses an electric polarization that can be reversed by an electric field. Collaborators in Taiwan created membranes of barium titanate just 40 nm thick and added miniature electrodes to create a tiny device, which was placed on a silicon substrate.
The researchers studied how the handedness of the atomic vibrations in the material changed as they flipped the electric polarization back and forth. When they reversed the electric polarization, the handedness of the phonons reversed too. Intriguingly, they found that the switched state persists after the electric field is removed.
The electric field therefore provides a reliable way to control the handedness of the phonons. Switching was achieved at room temperature using a voltage of just 3 V—two factors that could help with future integration into devices. The team was able to read out the handedness of chiral phonons using circularly polarized X-rays at the European Synchrotron Radiation Facility (ESRF) in Grenoble.
Here, the researchers used a technique known as resonant inelastic X-ray scattering (RIXS), which allowed them to resolve phonon chirality by seeing how angular momentum is transferred between circularly polarized X-rays and the lattice. "We now know that phonon angular momentum is something that can be controlled by electricity. This opens a pathway toward phonon-based information technologies," says Michael Grimes, first author of the paper at the PSI Center for Photon Sciences.
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